Inseminations at estrus induced by the presynch protocol before timed artification insemination

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Abstract:

A controlled field study examined conception
rates after two timed-AI (TAI) breeding
protocols conducted on two commercial dairy
farms. Estrous cycles in postpartum lactating
cows were presynchronized with two injections
of PGF2" given 14 days apart (Presynch) and
then, after 12 days, the standard Ovsynch protocol
(injection of GnRH 7 days before and 48 h
after an injection of PGF2", with one TAI at 12
to 16 hours after the second GnRH injection) or
Heatsynch protocol (injection of GnRH 7 days
before an injection of PGF2", followed 24 h later
by 1 mg of estradiol cypionate (ECP) and one
TAI 48 hours after ECP) was applied. Experimental
design allowed for AI to occur any time
after the second Presynch injection and during
the designed breeding week when estrus was
detected. Of the 1,846 first services performed,
only 1,503 (rate of compliance = 81.4%) were
performed according to protocol. Numbers of
cows inseminated, logistic-regression-adjusted
conception rates, and days in milk (DIM) were
for inseminations made: 1) during 14 days after
first Presynch injection (n = 145; 22.6%; 54 ±
0.4 DIM); 2) during 12 days after second Presynch
injection (n = 727; 33%; 59 ± 0.2 DIM);
3) during 7 days after the first GnRH injection
of Ovsynch or Heatsynch (n = 96; 32.1%; 74 ±
0.5 DIM); 4) after estrus as part of Heatsynch (n
= 212; 44.6%; 76 ± 0.3 DIM); 5) after TAI as
part of Heatsynch (n = 154; 21.1%; 76 ± 0.4
DIM); 6) after estrus as part of Ovsynch (n =
43; 48.7%; 77 ± 0.7 DIM); and 7) after TAI as
part of Ovsynch (n = 271; 24.4%; 77 ± 0.3
DIM). Conception rates when AI occurred after
one Presynch injection were less than when AI
occurred after two Presynch injections. Conception
rates for those inseminated after either
Presynch injection did not differ from those
inseminated after combined Heatsynch +
Ovsynch. Cows in the Ovsynch and Heatsynch
protocols inseminated after estrus during the
breeding week had greater conceptions rates
than those receiving the TAI, but overall conception
rates did not differ between protocols.
Among cows inseminated after detected estrus,
conception was greater for cows in the
Heatsynch + Ovsynch protocol (77 ± 0.4 DIM)
than for those inseminated after either Presynch
injection (54 ± 0.4 or 59 ± 0.2 DIM). We
concluded that conception rates after Heatsynch
and Ovsynch were similar under these experimental
conditions, and that delaying first AI
improved fertility for cows inseminated after
detected estrus.